a) Field of the Invention
The invention is directed to a method and an arrangement for the response analysis of semiconductor materials with optical excitation, wherein an electronic energy deposit is effected in an object by means of a laser beam and its relaxation is measured in the form of luminescent radiation exiting from the specimen.
b) Description of the Related Art
In practice, the aim of conducting an analysis of the recombination channels in solids, chiefly in semiconductors, with a high local resolution as it applies to measuring technology is currently approached by means of contacting methods as well as noncontacting methods.
The fundamental drawback in the electrical or photoelectrical methods which use simple modulation with lock-in detection (in the case of frequency domains) or with boxcar integration (in the case of time domains) consists in the required contact. With regard to noncontacting methods, the measurement of photoluminescence is one of the oldest procedures for characterizing radiant recombination (e.g., see W. D. Johnston, Appl. Phys. Lett. 33 (1978) 992). A modulated excitation ensures the required measuring sensitivity and a high local resolution is made possible by the selection of the modulation frequency as can be gathered, e.g., from an article by J. Marek in Appl. Phys. Lett. 49 (1986) 1732. The locally resolved photoluminescence is generally generated with low excitation densities of the charge carrier wave by means of modulated laser radiation. In so doing, an intensity evaluation will be subject to substantial errors and, as a rule, only spectroscopy will be carried out. In addition, modulation is limited to low frequencies because of the simple separation of the direct-light component.
Further, various processes of photothermal spectroscopy with high excitation energy are known from the prior art as noncontacting methods, for which U.S. Pat. No. 4,579,463, DE 40 35 266, and DE 42 23 337 can be cited as representative sources. A problem in these processes is the dominance of the thermal wave, whereby the influence of the thermal characteristics of the material predominates in the measured parameters and the effect of the charge carrier wave approaches zero with charge carrier lifetimes of less than 1 .mu.s. This drastically impairs the ability to determine electrical characteristics.